The invention is directed to a device for coating traveling material webs, and more specifically, the invention is directed to a device for coating a traveling material web wherein there is included two essentially horizontally opposed press rolls wherein at least one press roll is moveable relative to the other and wherein in conjunction with at least one press roll there is provided a coater that comprises a doctor blade.
A device for coating traveling material webs is previously known from the U.S. Pat. No. 4,259,921. This device is suited for performing both the sizing of the paper where the paper web is passed through a coating gap formed between two press rolls, and for performing a coating operation on both sides of the paper web. For the latter purpose, a sump is formed on one of the press rolls on its side facing away from the press gap through which the paper web is passed from above and which on the other end is defined by a doctor blade and its support which removes excess coating mixture from the web. First, this arrangement has the disadvantage that the coating thickness on the two different sides cannot be regulated separately. Second, this arrangement possesses the still greater disadvantage that while the web is passing through the sump the moisture of the coating mixture can for an extended time penetrate the paper from both sides resulting in a break of the paper web. Basically, this arrangement has the disadvantage that it requires an extremely accurate monitoring of the doctor blade angle relative to the tangent with the press roll at the point and/or line of contact with the doctor blade, and an extremely accurate monitoring of the angle at which the material web leaves the pressure roll and/or the doctor blade.
Various coaters are known wherein the coating mixture applied in excess is subsequently removed down to the desired coating thickness from the paper web passing over the press roll with the aid of a doctor blade. In such a process, appropriate nozzle applicators according to the U.S. Pat. No. 4,250,211 or other nozzle applicators featuring a pressure channel according to U.S. Pat. No. 3,418,970 are recommended for the coating devices. A favorable blade coater is also shown by the U.S. Pat. No. 4,169,425.
Such coating devices occupy a rather large space, and this is especially true when both sides of the paper web are to be coated as shown in the publication Pulp and Paper International 1966, pages 65 through 70. Such systems may occupy even more space when such a system provides for the operation of both a coating device and the previously mentioned sizing press. In paper production, customer requirements vary so that the papermaker must be prepared to accommodate these various requirements.